1. Field of the Invention
The invention relates to a process for preparing granulated supported manganese catalysts in aggregated form which catalysts, when formulated with peroxygen compounds, promote bleaching of flexible and hard surface substrates.
2. The Prior Art
Dry bleaching powders, such as those for cleaning laundry, generally contain inorganic persalts as the active component. These persalts serve as a source of hydrogen peroxide. Normally, persalt bleach activity in aqueous solution is undetectable where temperatures are less than 100.degree. F. and delivery dosages less than 100 ppm active oxygen. The art has recognized, however, that bleaching under such mild conditions may be effectuated through the use of activators.
Manganese (II) salts have been reported to be exceptionally effective in activating persalts under mild conditions. U.S. Pat. No. 4,481,129 discloses bleach compositions containing manganese (II) salts in conjunction with carbonate compounds. U.S. Pat. No. 4,478,733 describes bleach compositions containing manganese (II) salts in conjunction with aluminosilicate cationexchange materials. U.S. Pat. No 4,488,980 reports a bleach beneficial interaction between a condensed phosphate/alkali metal orthophosphate mixture and manganese (II) salts.
Bare heavy metal cations as disclosed in these patents, even when chelated, accelerate wasteful peroxide decomposition reactions that are non-bleach effective. Under alkaline conditions, as when used with laundry cleaning compositions, metal cations undergo irreversible oxidation and no longer catalyze. Perversely, the peroxide bleaching reaction is most effective at high pH.
Another problem with bare cations such as manganese (II) is that when utilized for whitening laundry, the free manganese ions deposit on the fabric. Strong oxidants, such as hypochlorites, are frequently included in laundry washes. Manganese ions will react with these strong oxidants to form highly staining manganese dioxide.
Stain problems resulting from free manganese ions have been overcome by binding the heavy metal ion to a water-insoluble support. Thus, European Patent Application No. 0 025 608 reveals a peroxide decomposition catalyst consisting of zeolites whose cations have been exchanged for heavy metals such as manganese. Co-pending U.S. patent application Ser. No. 597,971 discloses an activator comprising a water-soluble manganese (II) salt adsorbed onto a solid inorganic silicon support material, the combination having been prepared at a pH from 7.0 to 11.1.
In European Pat. No. 0 072 166, it was proposed to pre-complex catalytic heavy metal cations with a sequestrant and dry-mix the resultant product, in particulate form, with the remainder of the peroxygen containing detergent composition. Storage stability was found to be thereby improved. The patent notes that the complex of catalytic heavy metal cation and sequestrant can be agglomerated in a matrix of pyrophosphates, orthophosphates, acid orthophosphates and triphosphates.
While the foregoing systems provide adequate bleaching, three further problems must still be overcome. Upon storage, the catalyst and peroxide bleach particles interact resulting in loss of bleach activity during storage. Secondly, the catalyst particles are in the form of a fine powder. When blended with detergent granules, the catalyst powder is easily segregated falling to the bottom of the detergent package. A final problem is the formation of brown manganese dioxide in the detergent package during storage. Not only does the blend become aesthetically unpleasing, but manganese dioxide can deposit on fabric substrates during washing giving unsightly brown stains.
Co-pending U.S. patent application Ser. No. 668,536 reports solving the foregoing problems by binding manganese (II) cations to a "ligand" such as zeolite to form a complex. This complex is then protectively enclosed in a matrix of water-soluble or waterdisplacable materials. Examples of suitable coatings include modified starch, polyvinyl pyrrolidone, polyvinyl alcohol and sodium carboxymethyl cellulose. Most coating techniques were said to be suitable including pan-granulation, rolling drum blending, spray-drying and extrusion.
A further investigation of the aforementioned invention has found that not all protective coatings are readily shed when the granules are dispersed in water. Both the physical form and process conditions are now known to have an important influence on the performance of the resultant catalyst. The catalyst particles must release the manganese/aluminosilicate grains from the matrix within a prescribed time. When used with automatic washing machines, release must occur within minutes of water contact.
Consequently, it is an object of the present invention to provide a process to prepare a bleach catalyst of improved package storage stability that rapidly releases active partially manganese exchanged aluminosilicate particles upon dispersion in water